Fix stale CI stub values and false claims in Copilot instructions

[tas50]

Summary

CI stub (ci-main-pull-request-stub-1.0.7.yml)

• Version sent to SBOM/BlackDuck — it was hardcoded to '3.1.3' while the gem is at 3.1.10. The shared workflow's detect-version-source-type: file looks like the fix, but its set-application-version job is a placeholder that only echoes its inputs and never reads the file. Instead, the detect-custom-metadata job now reads VERSION, which Expeditor bumps on every merge, and passes it to the version input.
• Go commands — polaris-coverity-build-command: 'go build -o bin/chef-cli.exe' and 'go clean' were left over from another project. They are blanked, along with the commented-out Go equivalents. Polaris is disabled, so this doesn't change current behaviour, but it stops them running if Polaris is ever turned on.
• Deprecated ::set-output — switched to writing $GITHUB_OUTPUT.

.github/copilot-instructions.md

Corrected statements that aren't true of this repo:

• It named ci-main-pull-request-checks.yml, which doesn't exist. It now lists the real workflow files and what each one runs.
• It required >80% test coverage and coverage reports, but no coverage tool is configured.
• It told contributors to run bundle exec cucumber, which fails: cucumber isn't in the bundle. The test step is now bundle exec rake, which runs style and spec.
• It listed Expeditor: Skip Habitat / Skip Omnibus labels, which .expeditor/config.yml doesn't define.
• It promised "License compliance checks", but license_scout is false. That line is replaced with the scans the pipeline actually runs.

Added allchecks and Rovo to the cspell word list, since this PR edits the file that contains them.

Testing

• Parsed the workflow YAML and ran actionlint. The only notes are shellcheck quoting suggestions on lines this PR doesn't touch.
• cspell is clean on the changed Markdown.